Kendall, 20, and Kylie Jenner, 18, may be in for some bad news very soon! Big sister Kourtney Kardashian, 36, is allegedly having a baby with Justin Bieber, 22, who just happens to be both girls’ ex! Once they hear about Baby Biebs, they’re not going to play nice with Kourtney, according to a source who spoke to Life & Style magazine!